Final answer:
The purpose of the state primaries or caucuses is primary elections. These elections select one candidate from each party to run in the general election.
Step-by-step explanation:
The purpose of the state primaries or caucuses determining presidential nominees over 5-6 months, starting in late January of the election year, is c) Primary elections.
Primary elections are held by state political parties to select one candidate from each party who will run in the general election. These primaries offer tests of candidates' popular appeal and help determine the candidate who will receive the party's nomination. The primary election season allows candidates to campaign and gain support from voters across different states before the general election.